Scenario: Deploying an appliance as a distributed content site accelerator

About this scenario

In this scenario, a large media site/hosting provider is interested in caching so that it can

Constrain the cost of bandwidth
Scale sites that are growing rapidly
Secure the site content by putting the accelerator outside the firewall and the Web or streaming server inside the firewall

Illustration of the scenario topology

The following illustration shows this provider's deployment, which includes two appliances, one in the U.S.A. and one in Europe, running as accelerators.

About bandwidth savings with this deployment

An accelerator is deployed in Europe so that data from the Web site or streaming media site can be cached locally, thus saving expensive bandwidth, latency, or both. Initially, the European accelerator must obtain the Web objects or streaming media, thus incurring bandwidth costs. However, after the objects are in the cache in Europe, the objects can be served locally until they become stale. If the appliance determines that an object is stale, it fetches a newer version of the object from the Web server or streaming server.

U.S.A. and European accelerator configuration

The following table shows the accelerator options in the Appliance Manager that you would configure for each accelerator, and shows the host names of each accelerator. In this example, no restrictions were set on which IP addresses or netmasks could access the accelerators.

Option	Configuration data for the accelerator in the U.S.A.	Configuration settings for the accelerator in Europe
Host Name	www.abc.com	www-europe.abc.com
Primary IP Address	IP address A	IP address Z

After setup, you can change the Primary IP Address option (on the Network - Interfaces page) and host name option (on the System - Host Name page) in the Appliance Manager.

U.S.A. acceleration rule

The following acceleration rule is configured on the accelerator in the U.S.A.

Accelerator				Web server
IP	Port	Host	Path	IP/DNS Host	Port	Host	Path
*	80	www.abc.com	*	*	8080	www.internal.abc.com	*

European acceleration rule

The following acceleration rule is configured on the accelerator in Europe.

Accelerator				Web server
IP	Port	Host	Path	IP/DNS Host	Port	Host	Path
*	80	www.europe.abc.com	*	www.abc.com	80	www..abc.com	*

In the preceding rule on the European accelerator, the U.S.A. accelerator, www.abc.com is specified. In this case, if the European accelerator does not have a requested object in its cache, it sends a request to the U.S.A. accelerator to obtain the object. This method is preferable because you do not have the cost of the slow firewall or the bottleneck that prompted the deployment of the U.S.A. accelerator.

Note that the U.S.A. accelerator, www.abc.com, is not a parent to the European accelerator. You simply point the European accelerator to the U.S.A. accelerator instead of pointing it to the actual Web server or streaming server. The European accelerator is not aware of the U.S.A. accelerator, just as a user would not be aware of its presence.

Getting requests to the appropriate accelerator

One of the goals for this scenario is to reduce bandwidth cost. Therefore, the administrator wants to make sure that the users are sending requests to the closest accelerator. Assume for this configuration example that the administrator will inform users what URL to enter. The administrator instructs users in Europe to enter http://www-europe.abc.com/ and instructs users in the United States to enter http://www.abc.com/.

Note
There are a number of other ways to enable requests to reach the appropriate accelerator. For example, you could use DNS routing, or you could use a product such as 3DNS (from F5 Lab) or Distributed Director (from Cisco) that can distribute requests to the closest accelerator.